Heavy-duty drills using rotatable bits for penetrating into the earth enjoy widespread use. Recently, significant attention has been given to the use of feedback control to make the drilling operation more efficient, especially when drilling hard material (e.g., rock). By using such feedback control, the drilling operation can be continuously monitored and adjusted to ensure that the correct amount of thrust is applied or the rotational speed of the drilling element (bit) is maintained at the most efficient level to maximize the material removed per revolution, to avoid unnecessary grinding of the material, and to extend the service life of the bit. Examples of such feedback control systems can be found in commonly assigned U.S. Pat. Nos. 6,216,800 and 6,637,522, the disclosures of which are incorporated herein by reference. As an adjunct to sensing or measuring the thrust force and rotational speed, the torque acting on the drill bit can also be estimated and used to prevent overloading on the associated rotational motor.
A known manner of assessing the thrust acting on the drill bit and the rotational speed involves sensing or measuring characteristics of the hydraulic fluid used to power the drill. For example, the pressure in the fluid may be measured by a sensor (transducer) to obtain a signal proportional to the thrust acting on the drill bit. Likewise, the velocity of the hydraulic fluid flowing to the motor for rotating the bit may be measured using a sensor to obtain a signal proportional to the rotational speed. One or both “feedback” signals may then be used to monitor the drilling operation and make any adjustments necessary to maximize efficiency and extend the life of the drill bit.
In the past, the feed pressure and velocity sensors associated with the supply of hydraulic fluid to the drill head were “hardwired” to an input board. The input board transmitted the output signals over wires connected to a remote controller or computer elsewhere on the corresponding drilling machine for providing the desirable feedback control. In the harsh environment where earth (e.g., rock or coal) drilling usually takes place (e.g., in underground mines), the wiring is readily susceptible to being damaged. Even minor damage may render the feedback control totally useless.
A more conventional manner of measuring the rotational speed employs sensors mounted external on the drill head adjacent to the bit to measure physically the rotational speed or the thrust acting on it. However, such sensors must be calibrated frequently to compensate for machine variances. Like the fluid pressure and velocity sensors mentioned in the foregoing discussion, the external sensors are also susceptible to being damaged as the result of the conditions under which the drilling machine is typically used.
Accordingly, a need is identified for one or more embodiments of an instrumented drill head that eliminate the foregoing limitations and problems, either singularly or collectively.